1. Field of the Invention
The present invention relates to vent valves; and more particularly, to vent valves which include a thin film material covering one or more apertures.
2. Description of the Prior Art
Vent valves include ball check valves, rubber duckbill valves, rubber umbrella valves, and thin film valves. Ball check valves which utilize molded plastic balls or rubber balls are often unreliable, since such balls tend to be non-round. Compliant rubber balls can correct for their shape imperfections, but can wedge into their seats and become unresponsive to the low pressure differentials common to vent valves. Metallic balls are often more spherically shaped but can be expensive and/or subject to corrosion. In addition, metallic balls may not provide seals under low pressure differentials unless they are spring-loaded against their seats.
Rubber duckbill and rubber umbrella valves are molded parts that rely on their resilience to provide a normally closed air-tight seal. An advantage of duckbill and umbrella valves is that they can provide air venting under the relatively low pressure differentials common to vent valves. The resiliency of such valves, however, means they can be easily distorted, and such distortions can result in leakage. Moreover, such valves are relatively expensive.
Another class of vent valves are thin film valves. Such valves include a thin film of plastic material attached adjacent to one or more apertures such that the thin film material closes (thereby sealing) the apertures in response to a positive (i.e., superatmospheric) dispensing pressure in the bottle, and unseals the apertures in response to a negative (i.e., subatmospheric) pressure. An advantage of such thin film valves is that a very low cracking pressure will initiate venting. To date, however, the thin film material of such vent valves have typically been attached (via heat sealing or adhesive) to a flat, inner surface, of a bottle. Since installation of the thin film material is normally against an inner surface of the bottle, placement and attachment may be difficult operations and/or may require that the package be made of several components to allow ready access to the film installation point.